This invention relates to a sealing structure which may be used with hydraulically operated pistons or piston rods. It is particularly useful in sealing structures which alternately are exposed to high and low fluid pressures.
As noted in U.S. Pat. No. 3,909,016, entitled "Seal Assembly with Pivotable Slipper Seal", it is particularly difficult to obtain a good fluid seal, especially when the seal is subjected to high and low pressures alternately. To overcome that problem, that patent describes a device for use with two relatively movable machine parts. It uses a specially designed slipper seal, as a sealing member, in conjunction with an O-ring or other compressive force which are mounted in one of the machine parts. The device is designed in such a way that when it is subjected to low fluid pressure the slipper seal is in contact with the second machine part, such as a piston, through a corner of the slipper seal; this results in a very small frictional force but yet prevents leakage in the low pressure system. When the seal is subject to high fluid pressure, the compressive force of the O-ring is shifted to rotate the slipper seal and bring the entire surface of the slipper seal facing the second machine part into contact with that part. This surface of the slipper seal has no undercuts or voids so that it conforms to that surface of the second machine part.
A second sealing device is presented in U.S. Pat. No. 3,942,806, entitled "Sealing Ring Structure". In this patent, the low pressure contact point of the sealing member is defined by the intersection of a cylindrical recess which extends axially inwardly from one end of the sealing member and a radially inwardly inclined conical recess which extends axially inward from the opposite end of the sealing member. As with the invention in U.S. Pat. No. 3,909,061, under low fluid pressure, a sharp corner of the sealing member is in contact with the second machine part, but under high fluid pressure the entire face of the sealing member opposite the second machine part is compressed against that part.
A third U.S. Pat. No. 4,449,718, entitled "Packing for Hydraulic Pistons or Piston Rods" shows a modification of the device described in U.S. Pat. No. 3,942,806. The lower end of the radial face of the cylindrical recess is sloped to form a 45.degree. angle with the radial axis of the point contact. This is done to facilitate loading the packing ring onto the piston or other moving parts without distorting or damaging the contact area through material displacement.
A fourth U.S. Pat. No. 3,663,024 entitled "Sealing Assembly" shows a sealing member having a curvilinear configuration adopted to co-act with an O-ring to facilitate disposition of one member with the other.